Na₂WO₄, Na₂SO₄, hydrochloric acid (all analytically pure, Sinopharm Chemical Reagent Co., LTD.), toluene (Analytically pure, Tianjin Kemeiou Chemical Reagent Co., LTD.), and deionized water were used for the experiment.

Quanta 200 FEG Field Emission Environmental Scanning Electron Microscope (ESEM, FEI Company, USA); D/MAX-IIIA X-ray diffractometer (XRD, Shimadzu Company, Japan); VERTEX 70 Fourier Transform infrared spectrometer (BRUKER, Germany); UV550 UV-visible diffuse reflection spectrometer (DRS, JASCO, Japan); DF-101S collector thermostatic heating magnetic stirrer (Gongyi Yuhua Instrument Co., LTD.); TG-WS top high-speed centrifuge (Hunan Xiangyi Experimental Instrument Development Co., LTD.); XQ500W adjustable xenon lamp source (Shanghai Lansheng Electronics Co., LTD.).

Figure 1 shows the SEM photo of WO₃. According to Figure 1(a), the microstructure of WO₃ is corn-cob shape with good dispersion. It can be observed from Figure 1(b) that the length of nanorods is about 800nm, and the diameter is about 150 nm. The surface of the corn cob is uniformly covered with “corn kernels” with a diameter of about 20 nm.

Figure 2 is the X-ray diffraction pattern of WO₃ nanomaterials, from which

the crystal planes of (020), (200), (120), (112), (202), (122), (132), (004), (040), (114), (240) can be clearly seen, and each characteristic diffraction peak of the WO₃ standard card (JCPDS No. 20-1323) corresponded one to one, indicating that WO₃ nanomaterial was successfully synthesized. The shape of each diffraction peak is sharp, which indicates that the crystallinity of the prepared sample is good.

Figure 3 shows the infrared representation of WO₃ sample. The absorption peaks at 3443 and 1631 cm⁻¹ are attributed to surface hydroxyl and adsorbed water molecules [20] , respectively, while the infrared peaks at 2362 cm⁻¹ correspond to the adsorbed or trace CO₂ in the atmosphere [21] . It should be particularly pointed out that the peak at 856 cm⁻¹ is the characteristic peak of W-O bond [22] , indicating that the prepared sample is WO₃ nanomaterial. The upper part of the figure shows the infrared spectrum of the newly prepared WO₃ catalyst, and the lower part shows the infrared spectrum of the catalyst after the photocatalytic reaction for 8 h. It can be seen the position and intensity of each characteristic peak of the two spectral lines almost do not change, indicating that the WO₃ nanocatalyzer is relatively stable.

Figure 4 shows the UV-VIS diffuse absorption spectra of WO₃ sample. It can be seen from the figure that the samples have certain absorption intensity in the UV-visible region. And the absorption band edge is about 480 nm, indicating that the WO₃ sample has potential visible light catalytic activity.

Figure 5 shows the infrared spectra of toluene adsorbed on WO₃ catalyst every 5 min from toluene injection into the reactor to 30 min. As shown in the figure, in the full-band mid-infrared spectral region from 4000 to 400 cm⁻¹, toluene has characteristic infrared absorption in the regions of 3250 - 2750 cm⁻¹, 2000 - 1250 cm⁻¹, and 750 - 400 cm⁻¹, and the specific attribution is detailed below. According to the peak heights of each characteristic infrared peak in the figure, toluene

could reach the adsorption-desorption equilibrium on WO₃ catalyst within 30 min.

Figure 6 shows the infrared absorption spectra of toluene in various regions at different times after visible light catalytic degradation on WO₃ nanorods for 8 h with the extension of illumination time. In Figure 6(a), the peaks at 3073, 3043 and 3032 cm⁻¹ are attributed to the stretching vibration of C-H bond in benzene ring [23] , and the peaks at 2936 and 2880 cm⁻¹ are attributed to the stretching vibration peak of C-H bond in toluene methyl group [24] . In Figure 6(c), the peaks at 1948, 1860 and 1801 cm⁻¹ are attributed to the out-of-plane deformation vibration peaks of C-H bond on the benzene ring [25] , and the peaks at 1610 and 1498 cm⁻¹ are attributed to the stretching vibration of the benzene ring skeleton C=C [26] . In Figure 6(d), the infrared peak between 1089 and 1025 cm⁻¹ is attributed to the in-plane deformation vibration peak of C-H bond on the benzene ring [27] , and the peak at 729 and 695 cm⁻¹ is attributed to the characteristic absorption peak of benzene ring mono-substitution [24] . As can be seen from the above three figures, with the increase of the photocatalytic reaction time, the peak heights of each characteristic peak of toluene gradually

decreased, indicating that toluene was effectively degraded on WO₃ nanorods catalyst. In addition, it is worth mentioning that as shown in Figure 6(b), the peaks at 2360 and 2340 cm⁻¹ are the characteristic peaks of CO₂ [21] . It can be clearly seen that with the prolongation of the reaction time, the peak height of the characteristic peaks of CO₂ increases significantly, indicating that CO₂ is the final product of toluene degradation catalyzed by visible light.

In addition, it should be particularly pointed out that several new infrared peaks appeared in the reaction process. The peak at 951 cm⁻¹ was attributed to the out-of-plane deformation vibration of O-H bond in carboxylic acid [28] , and the peak at 792 cm⁻¹ was attributed to the C-H deformation vibration of aldehyde [29] . According to previous reports [29] and the results of this paper, benzaldehyde and benzoic acid are intermediates of toluene photocatalytic reaction.